A power semiconductor module generally includes an insulating substrate on which a semiconductor chip acting as a semiconductor element is mounted. The semiconductor chip and a circuit board of the insulating substrate are electrically connected using a joining material such as solder, and via bonding wire or a conductive plate. The insulating substrate and the semiconductor chip are housed in a housing. An external terminal electrically connected to the insulating substrate in the housing extends further outward from the housing. The inside of the housing is sealed with a sealing material in order to increase insulation.
An example of an existing power semiconductor module is shown as a sectional view in FIG. 4.
A power semiconductor module 101 shown in FIG. 4 includes a metal base plate 102. An insulating substrate 103 is joined using a joining material 104 to the top of the base plate 102. The insulating substrate 103 includes an insulating plate 131, a metal plate 132 provided on one surface of the insulating plate 131, and a circuit board 133 which is provided on the other surface of the insulating plate 131 which forms a predetermined circuit. An example of insulating substrate 103 is a DCB (Direct Copper Bond) substrate.
A semiconductor chip 105 such as an IGBT (insulated gate bipolar transistor) is electrically and mechanically connected using a conductive joining material 106 to the circuit board 133.
A frame body 107 is provided on the periphery of the base plate 102, and joined using a joining material 108. In this way, a housing of the power semiconductor module 101 is formed. An external terminal 109 extending from the inner side to the outer side of the frame body 107 is integrated with the frame body 107. The external terminal 109 and an electrode on a front surface of the semiconductor chip 105 are electrically connected by a bonding wire 110.
The semiconductor chip 105 and the insulating substrate 103 are housed in a space enclosed by the frame body 107, and the space is filled with a sealing material 111. In this way, mutual isolation of the semiconductor chip 105, the insulating substrate 103, the base plate 102, and the external terminal 109 is secured.
A screw hole 107a is provided in the frame body 107. The power semiconductor module 101 is fixed to a cooling member 122 by inserting a screw 121 into the screw hole 107a and screwing into the cooling member 122. Heat radiating grease 123 is applied between the base plate 102 and the cooling member 122, whereby heat from the semiconductor chip 105 is efficiently transferred to the cooling member 122 via the insulating substrate 103. A thermally conductive sheet is sometimes used instead of the heat radiating grease 123.
Also, it has been proposed that a plurality of heretofore described kind of power semiconductor modules is connected in parallel using a bus bar (PTL 1).
A thermosetting resin such as an epoxy resin is sometimes used as the sealing member 111 which is filled inside the housing in order to improve the insulating performance of the heretofore described kind of power semiconductor module 101. Meanwhile, if a large amount of thermosetting resin is used in the housing as the sealing material 111, thermal stress is exerted when there is a thermal history in assembling the power semiconductor module 101, a temperature change in the external environment in using the power semiconductor module 101, or the like. This is because the linear coefficient of the thermosetting resin and the linear coefficients of other members differ considerably. Further, there is concern that breakage of the bonding wire 110, deformation of the base plate 102 or the frame body 107, or the like will occur due to the thermal stress.
Breakage of the bonding wire 110 causes an immediate failure of the power semiconductor module 101. Also, the degree of adhesion to the cooling member 122 decreases due to deformation of the base plate 102 or the frame body 107, whereby thermal resistance increases. Also, there is concern that an increase in thermal resistance will lead to a rise in the temperature of the semiconductor chip 105, causing a reduction in the long-term reliability of the power semiconductor module 101. Also, using a large amount of thermosetting resin also leads to a rise in cost and an increase in weight of the power semiconductor module 101.
There is a power semiconductor device in which a gel-form resin, for example silicone resin, is injected into a housing in two separate layers, wherein a first resin layer is injected as far as a position in which the resin does not contact an auxiliary lead terminal, and hardened (PTL 2). Also, there is a power semiconductor device in which a space is formed between the upper surface of a gel filling the interior of a receptacle and the lower surface of a sealing plate corresponding to an upper lid of the receptacle, and furthermore, an external terminal hole provided in the sealing plate is blocked with a hard resin (PTL 3).
However, the thermal resistance of the gel-form silicone resin used in PTL 2 and PTL 3 is inferior to that of a thermosetting resin. Also, the insulation of the silicone resin is not always sufficient in a power semiconductor module with high breakdown voltage. Also, the structure in PTL 3 in which the sealing plate hole is blocked with a hard resin is complex in the shape of the sealing plate, because of which the manufacturing cost rises.